As for forming thin films on substrates to produce semiconductor substrates such as IC and LSI, a sputtering process, a chemical vapor phase epitaxy process, a coating process, a plating process, etc. are known. If a proper process is selected from these processes according to the intended purpose, almost satisfactory substrates for producing electronic parts can be obtained.
In semiconductor substrates such as integrated circuit (IC) and large scale integrated circuit (LSI), however, realization of high-density integrated circuits has been made in recent years. On that account, multilayer interconnection technology has become indispensable. In order to realize the multilayer interconnection structure, it is necessary to completely planarize surfaces of layer insulating films formed between wirings.
As typical technology for the planarization, the following processes have been previously proposed.
(1) SOG (Spin-on-Glass) or PIQ (K. Sato, et al., "A Novel Planar Multilevel Interconnection Technology Utilizing Polyimide", IEEE Trans. Part Hybrid Package, PHP-9, 176 (1973), PA1 (2) Etch back process (P. Elikins, et al., "A Planarization Process for Double Metal CMOS Using Spin-on Glass as A Sacrificial Layer", proceeding of 3rd International IEEE VMIC Conf., 100 (1986), PA1 (3) Lift-off process (K. Ehara, et al., "Planar Interconnection Technology for LSI Fabrication Utilizing Lift-off Process", J. Electrochem. Soc., vol. 131, No. 2, 419 (1984), PA1 (4) Bias sputtering process (C. Y. Ting, et al., "Study of Planarized Sputter-Deposited-SiO.sub.2 ", J. Vac. Sci. Tecnol. 15, 1105 (1978), Bias ECR process (K. Machida, et al., "SiO.sub.2 Planarization Technology with Biasing and Electron Cyclotron Resonance Plasma Deposition for Submicron Interconnections", J. Vac. Sci. Technol. B4, 818 (1986), and PA1 (5) Abrasion process (W. J. Patrick, et al., "Application of Chemical Mechanical Polishing to the Fabrication of VLSI Circuit Interconnections", J. Electrochem. Soc., Vol. 138, No. 6, June, 1778 (1991). PA1 a transfer thin film-forming step of applying a thin film-forming coating liquid to a continuously exposed surface of a thin film transfer base, to continuously form a transfer thin film on the thin film transfer base surface, PA1 a substrate feed step of continuously feeding a substrate onto the transfer base surface having the transfer thin film thereon, a surface of said substrate being to be provided with a thin film, and PA1 a transfer step of contacting the transfer base surface having the transfer thin film thereon with the substrate surface which is to be provided with the thin film, to continuously transfer the transfer thin film formed on the transfer base surface to the substrate surface. PA1 a coating liquid feed means for feeding a thin film-forming coating liquid onto a surface of a transfer roll, PA1 a transfer means including the transfer roll a surface which is coated with the thin film-forming coating liquid fed from the coating liquid feed means to form a transfer thin film, and PA1 a substrate conveying means for continuously conveying a substrate under the transfer roll, a surface of said substrate being to be provided with a thin film, PA1 wherein the transfer means is so fabricated that the transfer roll surface having the transfer thin film thereon is contacted with the surface of the substrate conveyed by the substrate conveying means, to transfer the transfer thin film formed on the transfer roll surface to the substrate surface. PA1 a sheet feed means for continuously feeding a sheet film, PA1 a coating liquid application means for applying a thin film-forming coating liquid to a surface of the sheet film fed, to form a transfer thin film, PA1 a substrate conveying means for continuously conveying a substrate under the sheet film, a surface of said substrate being to be provided with a thin film, PA1 a transfer means including a transfer roll for contacting the sheet film surface having the transfer thin film thereon, with the substrate surface which is to be provided with a thin film, to transfer the transfer thin film formed on the sheet film surface to the substrate surface, and PA1 a sheet recovery means for taking up the sheet film after the transferring.
Referring to the SOG (1), a SOG material comprising a coating liquid containing alkoxysilane such as Si(OR).sub.4 is applied onto a surface of a semiconductor substrate and then hardened by heating to form a planar film. In the SOG, the coating liquid is applied onto a substrate by spin coating, so that there exists a problem of safety or control of the coating liquid. Further, lowering of hot carrier resistance of MOS transistor caused by water content in the SOG film has been reported recently, and control of the water content has become a problem. Furthermore, since this process utilizes flowability of a coating, it is difficult to obtain a completely planar thin film.
The etch back process (2) is most widely used. This process, however, has a problem of occurrence of dust because a resist and an insulating film are etched at the same time. Therefore, this process is not easy in the dust control.
The lift-off process (3) has a problem of impossibility of lift off because a stencil material used is not completely dissolved in the lift-off stage. Because of insufficient controllability and yield, this process has not been practically used yet.
In the bias sputtering process and bias ECR process (4), film formation is made by sputtering or an ECR plasma CVD method. Additionally, RF bias is applied to produce sputtering on the substrate, and the protruded part is etched utilizing angle dependence of the sputtering to perform film formation, whereby planarization of the film is realized. The films obtained by these processes have high quality even if they are formed at a low temperature, and the planarization process is easy and simple. In these processes, however, the throughput is low and the elements may be damaged.
In the abrasion process (5), good planarity can be obtained, but an insulating film of high quality is necessary for the abrasion at a low temperature because an insulating film of poor quality cannot exhibit good abrasion properties. Moreover, because of unstable abrasion properties, a homogeneous thin film may be rarely obtained.
In the existing circumstances, diameters of semiconductor substrates (wafers) are becoming larger and larger, for example, from 8 inches to 12 inches. However, if the processes (1) to (5) are applied to the semiconductor substrates of large diameters, the controllability is insufficient, and it is difficult to ensure planarity of film and uniformity of film thickness.
The present invention has been made to solve such problems associated with the prior art as mentioned above, and it is an object of the invention to provide a continuous thin film-forming method, by which formation of a planar thin film on a substrate such as a semiconductor wafer can be carried out continuously, stably and at a low cost. In this method, quality lowering of the thin film and property change thereof with time, caused by adherence of impurities to the thin film or contamination of the thin film with impurities, are avoidable. Furthermore, this method is applicable to a large-sized substrate. It is another object of the invention to provide a thin film-forming apparatus for the method.